Pressing Alt and releasing does seem to highlight the File menu here (never noticed becasue I'm focused on the work, not the menus), but it doesn't open it or interfere in any way with combining it with any other key or mouse button.

Alt + Spacebar is another good one -- it temporarily gives you the hand tool (without highlighting the menu bar), and also lets you zoom with the scroll wheel. When you stop scrolling the hand tool is still there until you release the keys so you can adust the view position.